Modern aircraft often have more than one useable communications network through which to transmit and receive messages from terrestrial locations. At least one communications network is most preferred, e.g. because it has the lowest cost. As a result, messages are sent over the most preferred communications network to reduce cost. However, this can create a bottleneck which can delay the receipt of messages. If the messages are important, or if an emergency has arisen, then at least some of the messages need to bypass the bottleneck.